The present invention relates to a photomask inspection apparatus and, more particularly, to a photomask inspection apparatus to be used upon manufacturing semiconductor integrated circuit.
There are two inspection methods for inspecting a defect on a photomask. A first inspection method is a pattern comparison method in which adjacent unit patterns are compared with each other to inspect the difference therebetween. A second inspection method is a database verifying inspection method in which an actual pattern is compared with a design pattern to make an inspection.
A photomask inspection apparatus capable of simultaneously executing the inspections according to the above-mentioned two methods is disclosed in Japanese Patent Laid-Open Publication No. Hei 2-108947. FIG. 2 is a structural view of the apparatus disclosed by the above reference. As shown in the figure, a central control unit 12 operates so that a flush switch 3 turns on light sources 4R and 4L, and then optical signals D.sub.R1 and D.sub.L1 from right and left unit patterns 2R and 2L on a mask 2, which has been obtained through lenses 5R and 5L, are converted into comparison signals D.sub.R2 and D.sub.L2 by a photoelectric converting portion 6.
The comparison signal D.sub.R2 is subjected to intensity adjustment and division by an amplifier 13 and a division circuit 14 so as to be converted into signals D.sub.R3 and D.sub.R4 which are inputted into two comparators 9a and 9b respectively. The comparator 9a compares the comparison signal D.sub.L2 with the signal D.sub.R3 and stores defect information obtained by the pattern comparison method between the unit patterns 2L and 2R on the photomask 2 into a buffer memory 10a.
On the other hand, the comparator 9b compares the comparison signal D.sub.R4 with a comparison signal D.sub.2 which is generated by a design data converting portion 8 from design data D.sub.1 recorded in an external memory 7, and stores defect information obtained by the database verifying inspection method into a buffer memory 10b. When an output instruction is inputted from a console 1, each defect information stored in the buffer memories 10a and 10b is outputted to an external output unit 11.
However, in the above conventional photomask inspection apparatus, since the defect information shown in the external output unit 11 must be analyzed, there are some cases where it is difficult to determine which of adjoining chips contains defects such as an error in size of a contact hole.
Further, in the conventional photomask inspection apparatus, since the design data converting portion 8 must convert all the design data in the external output unit 11, there is a problem that a long time is required to convert the design data.